JPH10139989A - Poly(lactic acid)/polysaccharide composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a molding material, which is excellent in biodegradability and thermal resistance, at a low cost, by adding a polysaccharide at a specific stage of a process for carrying out ring-opening polymerization of a lactide utilizing a continuous reaction system. SOLUTION: In the process of ring-opening polymerization of a lactide, a polysaccharide powder is added at a stage where the conversion of a lactide to a polymer is 50 to 95%, and hereafter, the polymerization is continued to produce a poly(lactic acid)/polysaccharide composition. Usable polysaccharides include a cellulose substance derived from used paper, a piece of lumber from thinning, root, flue and the like; a hemicellulose derived from the husk of corn, the skin of barley, chaff and the like; starch; chitin and chitosan. A particle in an usable polysaccharide powder usually has a length along the longitudinal direction of 0.01 to 1mm. When the length is less than 0.01mm, the viscosity of the poly(lactic acid) reaction system mixed with a polysaccharide becomes too large to allow the polysaccharide to disperse with uniformity into the system, and further, such a large viscosity will result in an overload on the reaction equipment. When the length along the longitudinal direction of a polysaccharide particle is more than 1mm, a polysaccharide is difficult to be dispersed into the reaction system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition comprising polylactic acid and a polysaccharide or a substance containing a polysaccharide as a main component (hereinafter, simply referred to as a polysaccharide). The present invention provides a molding material having more excellent biodegradability and heat resistance than a simple mixture of the above.

[0002]

2. Description of the Related Art Polylactic acid is produced by ring-opening polymerization of lactide or direct polycondensation of lactic acid, and can be molded and processed by various methods, and is relatively excellent in biodegradability.
It is expected as a polymer that can respond to future environmental problems. For the purpose of reducing the cost of the polylactic acid and further improving the biodegradability, studies have been made to incorporate an inexpensive filler. Polylactic acid has an affinity for polysaccharides or substances containing polysaccharides as a main component, such as cellulose, hemicellulose, starch, and chitin. It is expected to lead to effective use of industrial waste, reduce costs and improve biodegradability.

However, in the conventional method of simply kneading polylactic acid and polysaccharide powder, only about 10% by weight of the polysaccharide can be blended. If it exceeds this, poor dispersion of the polysaccharide and thermal decomposition of the polymer during kneading will occur. And a good molded product could not be obtained.

[0004]

The object of the present invention is to find a method of blending a large amount of polysaccharide powder with polylactic acid, and to provide a molding material which is low in cost, excellent in biodegradability and heat resistance. Things.

[0005]

Means for Solving the Problems In the step of ring-opening polymerization of lactide using a continuous reaction apparatus, the present inventors add a polysaccharide powder when ring-opening polymerization has progressed beyond a certain conversion rate. Not only can a large amount of polysaccharide powder be added and compounded, but also the biodegradability and heat resistance of the molded product obtained from this compound are higher than the biodegradability and heat resistance of the molded product obtained from the simple kneading compound. They also found that they were much better and arrived at the present invention. That is, in the present invention, in the step of ring-opening polymerization of lactide using a continuous reaction apparatus, polysaccharide powder is added at a point in time when the polymerization conversion of lactide is 50 to 95%, and the ring-opening polymerization is continued. And a composition of polylactic acid and polysaccharide.

As a continuous reactor used for ring-opening polymerization of lactide, there is a device in which a plurality of reactors are arranged and a polymerization conversion rate is increased while sequentially moving the reactors. Such a device is used for opening a lactide solution. Used for ring polymerization. The polysaccharide powder is usually added in the last pot or the previous reaction pot.

A more general continuous ring-opening polymerization apparatus for lactide is a twin-screw kneader equipped with a vent mechanism, and lactide undergoes ring-opening polymerization while being extruded in a shaft. It is preferable that the two axes rotate in the same direction. When such an apparatus is used, a solvent is not necessarily required. The polysaccharide powder is usually introduced from an inlet provided before the final vent. The polysaccharide powder is added when the polymerization conversion of lactide is 50 to 95%, preferably 60 to 90%.

If the polymerization conversion is less than 50%, the lactide polymerization reaction may not proceed or the fluidity of the reaction system may be lost. If the polymerization conversion exceeds 95%, the powder is insufficiently dispersed and it is difficult to obtain a uniform composition.

The reactor is preferably replaced with an inert gas such as nitrogen gas in order to suppress thermal degradation of the polymer and to adjust characteristics such as molecular weight.

According to the method of the present invention, not only can a large amount of polysaccharide powder be added and blended, but also the biodegradability and heat resistance of a molded product obtained from this blend can be obtained from a simple kneaded blend. It is superior to the biodegradability and heat resistance of the molded product, but the reason is not clear. It is considered that part of lactide was graft-polymerized to the polysaccharide, and as a result, the affinity between polylactic acid and the polysaccharide powder was significantly improved.

In the ring-opening polymerization of lactide, a tin catalyst such as tin oxide, stannous chloride or tin dioctylate is usually used as a catalyst, and the reaction temperature is preferably about 190 ° C. If the temperature exceeds 200 ° C., the polysaccharide powder may be partially carbonized. In the ring-opening polymerization of lactide, glycolide may be copolymerized, or a low molecular weight polymer copolymerizable with lactide such as polyethylene glycol may be copolymerized as a modifier.

Examples of polysaccharides include waste paper, thinned wood,
Examples include cellulosic substances obtained from grasses, leaves, roots, cotton lint, and the like, hemicelluloses, starches, chitin, chitosan, and the like obtained from corn skin, bark, rice hulls, and the like.

The polysaccharide powder has a length in the major axis direction of 0.01 to
Although about 1 mm is usually used, it is preferably 0.02 to 0.5 mm in consideration of availability and the like. If the length in the major axis direction is less than 0.01 mm, when added to polylactic acid during ring-opening polymerization, the viscosity of the reaction system becomes too large, it becomes impossible to disperse uniformly, and the load on the reactor becomes too large. . On the other hand, if the length in the major axis direction exceeds 1 mm or more, it is difficult to disperse it in the reaction system. A plurality of polysaccharide powders may be used in combination.

In the polymerization of polylactic acid, if water is present in the reaction system, the polymerization reaction does not proceed. Therefore, the lactide and the polysaccharide powder added during the polymerization of polylactic acid are sufficiently dried beforehand to remove the water. Need to be kept.

[0015] The composition of polylactic acid and polysaccharide or a substance containing polysaccharide as a main component obtained by polymerization can be connected to a molding machine further to the end of the polymerization apparatus to perform desired molding continuously. It is good, but it is also possible to form pellets once with a pelletizer and to separately mold them.

The process of the present invention has made it possible to easily produce a polylactic acid composition containing a high proportion of polysaccharides, which was practically impossible with conventional methods.

[0017]

EXAMPLES The present invention will be described in further detail with reference to the following Examples, which do not limit the present invention.

[0018]

Example 1 Fully dried beforehand to reduce the water content to 100 pp
m or less, L-lactide having an optical purity of 99.5%
The L / D ratio was 42 and the screw diameter was 32 mm. At the same time, diocticle tin was added as a ring-opening polymerization catalyst in an amount of 0.3% to lactide, and the temperature of the barrel was reduced to 19%.
The temperature was kept at 0 ° C. to initiate ring-opening polymerization. At this time, nitrogen gas was supplied from the first vent hole, and exhaust was performed from the second vent hole. The two rotating shafts rotate in the same direction, and the rotation speed is 60r
pm.

A powder supply hole is provided between the first vent hole and the second vent hole, and the portion having a polymerization conversion of 75% is sufficiently dried in advance to have a water content of 100 ppm or less and a length in the long axis direction. Was crushed to 0.03 mm, and the same amount of lactide as waste paper was added. Unreacted lactide was recovered from the second vent at the same time as the evacuation. At the time when the polymerization reaction at the outlet of the extrusion reaction device was almost completed, a composition having a polylactic acid / waste paper ratio of 1/1 was obtained.

This polylactic acid and waste paper composition were subsequently connected to a pelletizer to obtain pellets containing 50% by weight of waste paper. A small amount of this pellet was taken, dissolved in chloroform, and the cellulose component as an insoluble component was separated and analyzed for weight. As a result, the cellulose component was 55% by weight. It is considered that a part of the lactide reacted with cellulose and was insolubilized in chloroform.

When the pellets were extruded at 190 ° C., a sheet having a thickness of 0.5 mm was easily obtained. 10
When the extruded sheet of cm × 10 cm was composted at 65 ° C., the original form was not retained after 3 weeks due to biodegradation.

Next, a cup having a thickness of 0.7 mm was formed by injection molding. This cup was placed in boiling water and boiled for 5 minutes, but no softening or deformation of the cup was observed.

[0023]

Comparative Example 1 A sheet having a thickness of 0.5 mm and a cup having a thickness of 0.7 mm were similarly obtained from polylactic acid pellets containing no waste paper.

When this cup was placed in boiling water and boiled for 5 minutes, the cup softened and deformed, and could not be put to practical use. Further, when the extruded sheet is composted at 65 ° C., biodegradation proceeds and the original form cannot be maintained.
It took a week.

[0025]

According to the present invention, a polylactic acid composition containing a large amount of a polysaccharide or a powder of a substance containing a polysaccharide as a main component by a specific production method is excellent in heat resistance, biodegradability and low cost molding material. It is. It has become possible to spread eco-friendly materials to the world.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // C08G 63/78 C08G 63/78

Claims (1)

[Claims] In the step of subjecting lactide to ring-opening polymerization using a continuous reactor, the polymerization conversion of lactide is 50 to 9%.
At the time of 5%, a polysaccharide or a powder containing a polysaccharide as a main component is added, and the ring-opening polymerization is continued to produce. Composition with a substance.